1. Field of the Invention
The present invention relates to an electric typewriter which is capable of making a correction with use of a correction tape, and more particularly, to a method for controlling the electric typewriter upon making such a correction.
2. Description of Prior Art
FIG. 1 is a perspective view of a conventional electric typewriter, FIG. 2 is a side view of the electric typewriter shown in FIG. 1.
In FIGS. 1 and 2, a printing paper 102 is set on a platen 101 which is rotated by a pulse motor (not shown). A carriage 103 is moved along a guide shaft 104 in the right and left directions by another pulse motor (not shown). A printing wheel 105 is rotatably supported by the carriage 103. The printing wheel 105 supports printing types 106 at respective free ends of flexible levers radially elongated from the center portion thereof. Upon printing a character on the printing paper 102, an ink ribbon 107 is arranged between the platen 101 and the printing type 106, and then, a hammer 109 is struck onto a printing type 106 positioned at the print position by an actuator 110, Thereafter the printing type 106 is struck onto the printing paper 102 together with the ink ribbon 107. However, upon making a correction, a correction tape 108 is set in place of the ink ribbon 107 so as to intervene between the printing wheel 105 and the platen 101, and then, the printing type 106 corresponding to a printed character to be erased is struck onto the intervening correction tape 108 a few times with use of the hammer 109 at the print position after positioning the printed character thereat.
In the aforementioned conventional electric typewriter, an operation of correction is controlled as shown in a timing chart of FIG. 3. In FIG. 3, (a) and (c) represent applied voltages to pulse motors for driving the carriage 103 and the printing wheel 105, respectively and (b) represents an applied voltage to a DC motor for shifting the ink ribbon 107 or the correction tape 108. Further, (d) represents pulses for driving the actuator 110 and (e) shows a vibration of the correction tape 108. As is apparent from FIG. 3, the movement of the carriage 103 to a position of the character to be corrected, the selection of the printing type 106 of the printing wheel 105 corresponding to the character to be corrected and the shifting operation of the correction tape 108 are all started at the same time t.sub.1. A first ready signal representing the completion of the movement of the carriage 103 is outputted at a timing t.sub.4. This occurs after a constant time interval from the stopping of a driving pulse to the pulse motor for the carriage 103. Then a second ready signal representing the completion of rotation of the printing wheel 105 is outputted at a time t.sub.2 after a constant time interval from the stopping of the driving pulse to the pulse motor for the printing wheel 105. These time intervals are predetermined time intervals in which oscillations of the carriage 103 and the printing wheel 105 might be stopped. On the other hand, a third ready signal representing the completion of the shifting operation of the correction tape 108 is outputted at a time t.sub.3, after the DC motor for driving the correction tape 108 has been braked. This is done by applying a negative voltage to the motor, as shown in (b) of FIG. 3. As shown in (d) of FIG. 3, three pulses for driving the hammer 109 are applied to the actuator 110 sequentially from the time t.sub.4 or after a start time interval therefrom since the first to third ready signals have not been outputted until then. When the selected printing type 106 of the printing wheel 105 is struck onto the character to be corrected, three times, through the correction tape 108 by the hammer 109, the printed ink of the character is adhered onto the correction tape 108. Thus, the correction of the character is made.
The timings at which time, when the ready signals of the carriage 103 and the printing wheel 105 are respectively outputted are different from one another depending on the amounts of the movements of the carriage 103 and the rotation angle cf the printing wheel 105 etc. . .
Conventionally, a timer for counting a predetermined time interval t.sub.0 is provided in order to avoid such a possibility that the printing type 106 would be struck while the oscillation of the correction tape 108 is still going on. The timer is started when all of the first to third ready signals have been outputted. Thus, the printing type is guaranteed to strike the character to be corrected after the oscillation of the correction tape 108 has stopped.
However, this method has such a disadvantage in that the ink adhered to the correction tape at the first stroke of the printing type is retransferred to the printing paper on the next stroke. This is because the position of the correction tape 108 struck at the next stroke is unchanged from that at the first stroke. This disadvantage is enhanced, especially in such an electric typewriter in that the correction position is automatically shifted from the former one, by a small distance, in order to avoid a possible miscorrection due to ar error in positioning the printing type over the character to be erased.